J. Nannoplankton Res. 31 (1), 2010, pp.1-4 © 2010 International Nannoplankton Association, Inc.
ISSN 1210-8049 Printed by The Sheridan Press, Hanover, PA, USA

1A new Oligocene Triquetrorhabdulus species, T. longus sp.
nov.
Teodora Blaj
Department of Geology & Geochemistry, Stockholm University, SE-106 91 Stockholm, Sweden; teodora@geo.su.se

Jeremy Young
Palaeontology Department, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK

Manuscript received 28th January, 2009; revised manuscript accepted 1st December, 2009

Abstract Whilst investigating the first occurrence of Triquetrorhabdulus carinatus at Ocean Drilling Program
Leg 199 Site 1218 in the palaeo-equatorial Pacific, a form that resembles this species was observed and counted separately. Based on differences in size, shape and stratigraphic range, compared to the typical T. carinatus, we describe
this longer morphotype as a new, and potentially biostratigraphically useful, nannolith species, T. longus sp. nov.

Keywords Nannolith, Oligocene, Triquetrorhabdulus, taxonomy, ODP Leg 199 Site 1218, palaeo-equatorial Pacific Ocean

1. Intoduction
Triquetrorhabdulus is an elongated, rod-shaped nannolith
formed of three blades (Young et al., 1997; Young, 1998).
T. carinatus was originally described from the westernequatorial Pacific Ocean as “forms elongated with bothends more or less pointed; the three calcite rods show thesame diameter when viewed from one end; they are placed
at 120˚ to each other. In polarized light, forms show maximum extinction when parallel to crossed nicols” (Martini,1965, p.408). The forms were described as varying inlength, between 9 and 15µm, although morphotypes up to24µm long were also observed (Martini, 1965).
The original description of the genus Triquetrorhabdulus was further developed by Bramlette & Wilcoxon(1967). They observed that “the optic axes of the calcite
are parallel to the long axis of the rod” (Bramlette &Wilcoxon, 1967, p.128). Lipps (1969, p.1030) noticed that“much variation in size and shape occurs among individual
specimens even in the same sample; some are short andtruncated at one end, whereas others may be nearly twice
as long and taper to a sharp point at each end”. Several
species of Triquetrorhabdulus have been described, basedon the extent of development of the ridges, as well as theirgeneral shape, and most of these have proved of stratigraphic value (Aubry, 1988; Young, 1998).
Two main morphotypes of ‘T. carinatus’ have been distinguished from Deep Sea Drilling Project (DSDP) Site
242 (Indian Ocean): long, thin specimens with parallelsides (complete specimens 25 to 50 x 1.5 to 2.5µm) andshorter, broader specimens with a distinct taper (15 to 25 x
2 to 4µm) (Young, 1987; www.nannotax.org). However,these morphotypes were not formally described as separate species. During a high-resolution biostratigraphic
study of the first occurrence (FO) of T. carinatus from
Ocean Drilling Program (ODP) Site 1218 in the palaeoequatorial Pacific Ocean, both morphotypes were encountered (Blaj et al., 2009). At this site, the Triquetrorhabdulus

morphotypes appeared to have distinct stratigraphic ranges
and morphologies, and so it was decided to describe theelongate form as a new, and potentially biostratigraphicallyuseful, species.
2. Material and methods
Originally, a suite of 537 samples was examined from acontinuous Oligocene section, in order to increase the number of useful biostratigraphic events in the Upper
Oligocene. The investigated section was recovered fromODP Site 1218 (8˚53.38’N, 135˚22.00’W; 4826m waterdepth; Figure 1) from the tropical Pacific Ocean (Lyle etal., 2002; Wilson et al., 2006) and corresponds to the timeinterval between 23.41 and 27.52Ma, based on the astronomically-calibrated time-scale of Pälike et al. (2006).

Figure 1: Location of ODP Site 1218 and DSDP Site 242. Map modifiedfrom http://www.iodp-usio.org/

Smear-slides were prepared from raw sediment samples using standard techniques, with the sediment smeared
over the glass microscope slide (Perch-Nielsen, 1985).
Semi-quantitative data on the Triquetrorhabdulus morphotypes (Figure 2) were obtained using the method ofBackman & Shackleton (1983), with abundance expressedBlaj, Young2

as number of specimens per mm2. In order to study in detail the morphological differences, 10 Oligocene samples
were selected for analysis using both transmitted light(LM) and scanning electron (SEM) microscopy. The SEM
work was performed using a Phillips XL30 Field Emission
SEM at the Natural History Museum, London. All 10 samples and the SEM and LM micrographs of the morphotypes
are archived at the Natural History Museum, London.

T. carinatus

distribution of the longer morphotype encompasses morethan 3Myr (from 27.5 to 24.0Ma, based on the Pälike et al.,2006, time-scale), representing the first reliable total range
documented for this morphotype. This morphotype has also
been observed in the Indian Ocean at DSDP Site 242(www.nannotax.org), suggesting a wide distribution. The
beginning of the peak abundance interval of T. carinatus
coincides with the decline in abundance of the longer morphotype. It seems reasonable to assume that ecological conditions at that time became more favourable tothe dominance of T. carinatus.
4. Taxonomic description
The terminology used here follows the guidelines forcalcareous nannofossil terminology proposed byYoung et al. (1997).
INCERTAE SEDIS
Family TRIQUETRORHABDULACEAE Lipps,
1969
Genus Triquetrorhabdulus Martini, 1965

T. longus

Triquetrorhabdulus longus sp. nov.
Pl.1, figs 1-13, 19-21
Derivation of name: From the Latin ‘longus’, meaning ‘long’, referring to the great length of the nannolith.
Diagnosis: A thin (<2µm), elongate (>15µm) species ofTriquetrorhabdulus formed of three calcite rods of similar
width. The c-axis is parallel to the length of the nannolith.
Differentiation: T. longus is primarily distinguishable fromT. carinatus Martini, 1965 by its greater length (comparePl.1, figs 14-19 with figs 22-24). The completely preserved
specimens are double the size of T. carinatus. T. longus isnarrower and less bright in XPL than T. carinatus, and differs from planktonic foraminifera spines in showing distinct taper.
Comments: Most observed specimens taper gradually towards one end, with the other end having a rather abrupt Vshaped termination (see Pl.1, figs 2-5, 8-13, 19-20).
However, a few of the longest specimens show a gradualtapering towards both ends (Pl.1, figs 1, 6).
Holotype: Pl.1, fig.20 (length = 25µm, width = 1.5µm).
Paratype: Pl.1, fig.4 (length = 28µm, width = 1.5µm).
Type locality: ODP Leg 199, Site 1218, central PacificOcean (8˚53.38’N, 135˚22.00’W).
Type level: Sample ODP 199, Hole 1218A-12H-04, 3536cm, Upper Oligocene.
Range: Restricted to NP24-25, Chattian, Upper Oligocene.
Occurrence: At Site 1218, T. longus occurs over a 3Myrinterval (based on the time-scale of Pälike et al., 2006) inthe Late Oligocene. Its FO has an age estimate of 27.5Ma.
This biohorizon is characterised by an interval of low anddiscontinuous abundance of the taxon, followed by its continuous and common presence at around 26.9Ma (FigureFigure 2: Abundance patterns of Triquetrorhabdulus longus (grey line) and T.
carinatus (black line) at Site 1218, expressed as number of specimens per mm2(from Blaj et al., 2009)

3. Results and discussion
While investigating the FO of Triquetrorhabdulus carinatus from Site 1218, a form that resembles this species wasobserved and counted separately (Blaj et al., 2009, fig.8).
This morphotype differs from typical T. carinatus in having a larger size. It can be up to 45µm long, in contrast totypical T. carinatus, which has a maximum length of 15µm.
Most observed specimens of the longer morphotype show
moderate calcite overgrowth. The ridges are present insome specimens, but are often too poorly preserved to beclearly observed. In cross-polarised light (XPL), the longer
morphotype appears greyish and less bright, suggesting that
it is less heavily calcified than T. carinatus. However, bothmorphotypes display similar optical behaviour, and show
maximum birefringence at 45˚ to the polarisers when observed in XPL. Complete specimens of this longer morphotype are needle shaped, with one end being thicker andbrighter, narrowing throughout its length and becoming
progressively less bright. Even when the specimens ascribable to the longer morphotype are broken, they are still
distinguishable from typical specimens of T. carinatus because their fragments are narrower and less bright.
T. carinatus and the longer morphotype show different
stratigraphic ranges (Figure 2) in the palaeo-equatorial Pacific Ocean. A crossover in abundance occurs just prior to25Ma, at which time the abundance of the longer morphotype decreases gradually, while T. carinatus increases distinctly in abundance. At Site 1218, the stratigraphic

A new Oligocene Triquetrorhabdulus

Plate 15µm (SEM)
T. longus Sample DSDP 242-8-2, 30-31cm

T. longus Sample ODP 1218A-12H-3, 105cm

T. longus Sample ODP 1218A-12H-5, 85cm

T. longus Sample ODP 1218A-12H-5, 135cm

T. longus Sample ODP 1218A-12H-4, 35cm

T. longus Sample ODP 1218A-14H-2, 75cm

T. longus Sample ODP 1218A-13H-6, 15cm

T. longus Sample ODP 1218B-13H-2, 45cm

T. carinatus Sample ODP 1218A-14H-2, 75cm

T. longus Sample ODP 1218A-12H-5, 135cm
T. carinatus Sample ODP 1218B-13H-2, 45cm

T. longus Sample ODP 1218A-12H-4, 35cm

T. longus Sample ODP 1218B-14H-3, 125cm

5µm (LM)T. longus Sample ODP 1218A-12H-4, 35cm

T. carinatus Sample ODP 1218B-11H-6, 3cm

34Blaj, Young2). The last specimens of T. longus were observed at
24.0Ma. Remarkably, the two nannoliths have different
stratigraphic ranges at Site 1218. Although T. longus and T.
carinatus show a partial overlap in the lower parts of theirranges, the former is always more abundant compared tothe latter (Figure 2). Towards the end of its range, T. longus
shows a decrease in abundance virtually coincident withthe onset of the peak abundance interval of T. carinatus.
Acknowledgements
This research received support from the SYNTHESYS Project(http://www.synthesys.info/), which is financed by European
Community Research Infrastructure Action under the FP6 Structuring the European Research Area Programme. The assistanceof Lauren Howard of the NHM EMMA unit is gratefully acknowledged. The valuable comments of Isabella Raffi, Milos Bartol and Jan Backman are thankfully acknowledged. We also thankour reviewers, Claudia Agnini and Mike Styzen, and the Editor,Jackie Lees, for their constructive comments and remarks.

References
Aubry, M.-P. 1988. Handbook of Cenozoic calcareous nannoplankton. Book 2: Ortholithae (Holococcoliths, Ceratolithsand others). Micropaleontology Press, New York, 279pp.
Blaj,. T., Backman, J. & Raffi, I. 2009. Late Eocene to Oligocene
preservation history and biochronology of calcareous nannofossils from paleo-equatorial Pacific Ocean sediments. Rivista
Italiana di Paleontología e Stratigrafía, 115(1): 67-85.
Bramlette, M.N. & Wilcoxon, J.A. 1967. Middle Tertiary calcareous nannoplankton of the Cipero section, Trinidad, W.I.
Tulane Studies in Geology and Paleontology, 5: 93-131.
Lipps, J.H. 1969. Triquetrorhabdulus and similar calcareous
nannoplankton. Journal of Paleontology, 43(4): 1029-1032.
Lyle, M., Wilson, P.A., Janecek, T.R. et al. 2002. Proc. ODP, Init.
Repts, 199. College Station, TX (Ocean Drilling Program),
doi:10.2973/odp.proc.ir.199.2002.
Martini, E. 1965. Mid-Tertiary calcareous nannoplankton from
Pacific deep-sea cores. Colston Papers, 17: 393-411.
Perch-Nielsen, K. 1985. Cenozoic calcareous nannofossils. In:H.M. Bolli, J.B. Saunders & K. Perch-Nielsen (Eds). Plankton Stratigraphy. Cambridge Univ. Press, Cambridge: 427554.
Pälike, H., Norris, R.D., Herrle, J.O., Wilson, P.A., Coxall, H.K.,
Lear, C.H., Shackleton, N.J., Tripati, A.K. & Wade, B.S.
2006. The heartbeat of the Oligocene climate system. Science,314: 1894-1898.
Wilson, P.A., Lyle, M. & Firth, J.V. (Eds) 2006. Proc. ODP, Sci.
Results, 199. College Station, TX (Ocean Drilling Program),
doi:10.2973/odp.proc.sr.199.2006.
Young, J.R. 1987. Neogene calcareous nannofossils from the
Makran Region of Pakistan and the Indian Ocean. Unpublished PhD thesis, Imperial College London, London: 288pp.
Young, J.R. 1998. Neogene. In: P.R. Bown (Ed.). CalcareousNannofossil Biostratigraphy. British MicropalaeontologicalSociety Publication Series, Chapman & Hall/Kluwer Academic Publishers, London: 225-265.
Young, J.R., Bergen, J.A., Bown, P.R., Burnett, J.A., Fiorentino,A., Jordan, R.W., Kleijne, A., van Niel, B.E., Romein, A.J.T.
& von Salis, K. 1997. Guidelines for coccolith and calcareous
nannofossil terminology. Paleontology, 40: 875-912.